This patent application claims priority from a Japanese patent application No. 2001-109566 filed on Apr. 9, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an inverter device. More particularly, the present invention relates to an inverter device in which two switching devices are connected in series and which supplies an alternating power generated at a connection point of these two switching devices to a load.
2. Description of the Related Art
The inverter device changes a direct voltage of a power source to an alternating voltage and supplies the alternating voltage to the load. An exemplary application of the inverter device is lighting equipment using a discharge lamp such as a metal halide lamp as a light source.
As the inverter device, an inverter device including a plurality of switching devices arranged to form a half-bridge arrangement and an inverter device including the switching devices arranged to form a full-bridge arrangement are known. In these bridge arrangements, a situation where all the switching devices are in an simultaneous-on-state may occur. This situation easily occurs when the respective switching devices are switched from an on state to an off state or from the off state to the on state. This situation causes the degradation of electrical efficiency and abnormal heat generation.
For example, Japanese Utility Model Application Laid-Open No. 6-9097 describes a structure for generating dead time in a pulse signal generator for generating a pulse signal, in order to prevent the aforementioned situation.
However, the structure for generating the dead time in the pulse signal generator is complicated. Moreover, the required number of parts is large.
Therefore, it is an object of the present invention to provide an inverter device, which is capable of overcoming the above drawbacks accompanying the conventional art. The above and other objects can be achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
According to the first aspect of the present invention, an inverter device, including a first series circuit having first and second switch units connected in series and a pulse signal generator operable to generate a pulse signal, for supplying an alternating voltage to a load by alternately driving the first and second switch units to be turned on and off in accordance with the pulse signal while a direct voltage is applied to the first series circuit, the inverter device comprises: a first driving controller operable to generate a first driving signal and to drive the first switch unit based on the first driving signal, the first driving signal rising with a first speed at a rising of the pulse signal in a direction for turning on the first switch unit and falling with a second speed at a falling of the pulse signal in a direction for turning of the first switch unit, the second speed being higher than the first speed; and a second driving controller operable to generate a second driving signal and to drive the second switch unit based on the second driving signal, the second driving signal falling with a third speed at the rising of the pulse signal in the direction for turning on the first switch unit and rising with a fourth speed at the falling of the pulse signal in the direction for turning off the first switch unit, the third and fourth speeds being between the first and second speeds.
The load may be connected between the first and second switch units at one end and is connected to a reference potential at the other end.
The first driving controller may include a resistor element provided on a line of the pulse signal and a capacitor element connected between the resistor element and the first switch unit at one end; the second driving controller may include a resistor element provided on the line of the pulse signal and a capacitor element connected between the resistor element of the second driving controller and the second switch unit at one end; and a first product of an equivalent resistance value of the resistor element of the first driving controller with respect to an electric current seen from the direction for turning on the first switch unit and a capacitance of the capacitor element may be larger than a second product of an equivalent resistance value of the resistor element of the second driving controller with respect to an electric current seen from the direction for turning off the second switch unit and a capacitance of the capacitor element.
The first driving controller may include a resistor element provided on a line of the pulse signal and a capacitor element connected between the resistor element and the first switch unit at one end; the second driving controller may include a resistor element provided on the line of the pulse signal and a capacitor element connected between the resistor element of the second driving controller and the second switch unit at one end; and a third product of an equivalent resistance value of the resistor element of the first driving controller with respect to an electric current seen from the direction for turning off the first switch unit and a capacitance of the capacitor element may be smaller than a fourth product of an equivalent resistance value of the resistor element of the second driving controller with respect to an electric current seen from the direction for turning on the second switch unit and a capacitance of the capacitor element.
The first switch unit may include a first main switch and a first switch driving unit operable to drive the first main switch in accordance with the first driving signal, and the second switch unit may include a second main switch and a second switch driving unit operable to drive the second main switch in accordance with the second driving signal.
The inverter device may further comprise: a second series circuit, arranged in parallel to the first series circuit, including a third switch unit and a fourth switch unit; a third driving controller operable to generate a third driving signal based on the pulse signal and to drive the third switch unit based on the second driving signal, the third driving signal falling with the third speed at the rising of the pulse signal in the direction for turning on the first switch unit and rising with the fourth speed at the falling of the pulse signal in the direction for turning off the first switch unit; and a fourth driving controller operable to generate a fourth driving signal and to drive the fourth switch unit based on the first driving signal, the fourth driving signal rising with the first speed at the rising of the pulse signal in the direction for turning on the first switch unit and falling with the second speed at the falling of the pulse signal in the direction for turning off the first switch unit, wherein the load is connected between the first and second switch units at one end and is connected between the third and fourth switch units at the other end, and a pair of the first and fourth switch units and a pair of the second and third switch units are alternately driven to be turned on and off in accordance with the first, second, third and fourth driving signals.
The first driving controller may include a resistor element provided on a line of the pulse signal and a capacitor element connected between the resistor element and the first switch unit at one end; the second driving controller may include a resistor element provided on the line of the pulse signal and a capacitor element connected between the resistor element of the second driving controller and the second switch unit at one end; the third driving controller may include a resistor element provided on the line of the pulse signal and a capacitor element connected between the resistor element of the third driving controller and the third switch unit at one end; the fourth driving controller may include a resistor element provided on the line of the pulse signal and a capacitor element connected between the resistor element of the fourth driving controller and the fourth switch unit at one end; a first product of an equivalent resistance value of the resistor element of the first driving controller with respect to an electric current seen from the direction for turning on the first switch unit and a capacitance of the capacitor element of the first driving controller may be larger than a second product of an equivalent resistance value of the resistor element of the second driving controller with respect to an electric current seen from the direction for turning off the second switch unit and a capacitance of the capacitor element of the second driving controller; and a third product of an equivalent resistance value of the resistor element of the fourth driving controller with respect to an electric current seen from the direction for turning on the fourth switch unit and a capacitance of the capacitor element of the fourth driving controller may be larger than a fourth product of an equivalent resistance value of the resistor element of the third driving controller with respect to an electric current seen from the direction for turning off the third switch unit and a capacitance of the capacitor element of the third driving controller.
The first driving controller may include a resistor element provided on a line of the pulse signal and a capacitor element connected between the resistor element and the first switch unit at one end; the second driving controller may include a resistor element provided on the line of the pulse signal and a capacitor element connected between the resistor element of the second driving controller and the second switch unit at one end; the third driving controller may include a resistor element provided on the line of the pulse signal and a capacitor element connected between the resistor element of the third driving controller and the third switch unit at one end; the fourth driving controller may include a resistor element provided on the line of the pulse signal and a capacitor element connected between the resistor element of the fourth driving controller and the fourth switch unit at one end; a fifth product of an equivalent resistance value of the resistor element of the first driving controller with respect to an electric current seen from the direction for turning off the first switch unit and a capacitance of the capacitor element of the first driving controller may be smaller than a sixth product of an equivalent resistance value of the resistor element of the second driving controller with respect to an electric current seen from the direction for turning on the second switch unit and a capacitance of the capacitor element of the second driving controller; and a seventh product of an equivalent resistance value of the resistor element of the fourth driving controller with respect to an electric current seen from the direction for turning off the fourth switch unit and a capacitance of the capacitor element of the fourth driving controller may be smaller than an eighth product of an equivalent resistance value of the resistor element of the third driving controller with respect to an electric current seen from the direction for turning on the third switch unit and a capacitance of the capacitor element of the third driving controller.
The first switch unit may include a first main switch and a first switch driving unit operable to drive the first main switch in accordance with the first driving signal; the second switch unit may include a second main switch and a second switch driving unit operable to drive the second main switch in accordance with the second driving signal; the third switch unit may include a third main switch and a third switch driving unit operable to drive the third main switch in accordance with the third driving signal; and the fourth switch unit may include a fourth main switch and a fourth switch driving unit operable to drive the fourth main switch in accordance with the fourth driving signal.
The summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the features described above. The above and other features and advantages of the present invention will become more apparent from the following description of the embodiments taken in conjunction with the accompanying drawings.